[Intel-gfx] [PATCH] drm/i915: Specify bsd rings through exec flag

[Zhipeng Gong]

On Skylake GT3 we have 2 Video Command Streamers (VCS), which is asymmetrical.
For example, HEVC GPU commands can be only dispatched to VCS1 ring.
But userspace has no control when using VCS1 or VCS2. This patch introduces
a mechanism to avoid the default ping-pong mode and use one specific ring
through execution flag. This mechanism is usable for all the platforms
with 2 VCS rings.

v2: fix whitespace (Rodrigo)
v3: remove incorrect chunk that came on -collector rebase. (Rodrigo)
v4: change the comment (Zhipeng)

Signed-off-by: Zhipeng Gong <zhipeng.gong at intel.com>
Reviewed-by-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 19 +++++++++++++++++--
 include/uapi/drm/i915_drm.h                |  8 +++++++-
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 0c25f62..de652a5 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -1317,8 +1317,23 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 	else if ((args->flags & I915_EXEC_RING_MASK) == I915_EXEC_BSD) {
 		if (HAS_BSD2(dev)) {
 			int ring_id;
-			ring_id = gen8_dispatch_bsd_ring(dev, file);
-			ring = &dev_priv->ring[ring_id];
+
+			switch (args->flags & I915_EXEC_BSD_MASK) {
+			case I915_EXEC_BSD_DEFAULT:
+				ring_id = gen8_dispatch_bsd_ring(dev, file);
+				ring = &dev_priv->ring[ring_id];
+				break;
+			case I915_EXEC_BSD_RING1:
+				ring = &dev_priv->ring[VCS];
+				break;
+			case I915_EXEC_BSD_RING2:
+				ring = &dev_priv->ring[VCS2];
+				break;
+			default:
+				DRM_DEBUG("execbuf with unknown bsd ring: %d\n",
+					  (int)(args->flags & I915_EXEC_BSD_MASK));
+				return -EINVAL;
+			}
 		} else
 			ring = &dev_priv->ring[VCS];
 	} else
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 2502622..fcb16bf 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -737,7 +737,13 @@ struct drm_i915_gem_execbuffer2 {
  */
 #define I915_EXEC_HANDLE_LUT		(1<<12)
 
-#define __I915_EXEC_UNKNOWN_FLAGS -(I915_EXEC_HANDLE_LUT<<1)
+/** Used for switching BSD rings on the platforms with two BSD rings */
+#define I915_EXEC_BSD_MASK		(3<<13)
+#define I915_EXEC_BSD_DEFAULT		(0<<13) /* default ping-pong mode */
+#define I915_EXEC_BSD_RING1		(1<<13)
+#define I915_EXEC_BSD_RING2		(2<<13)
+
+#define __I915_EXEC_UNKNOWN_FLAGS -(1<<15)
 
 #define I915_EXEC_CONTEXT_ID_MASK	(0xffffffff)
 #define i915_execbuffer2_set_context_id(eb2, context) \
-- 
2.0.4